The role of altered microRNA expression in premalignant and malignant head and neck lesions with epithelial origin

Abstract Background and Aims The premalignant lesions of the oral cavity carry a risk of transformation to malignancy. Hence, early diagnosis followed by timely intervention remarkably affects the prognosis of patients. During tumorigenesis, particular microRNAs (miRNAs) show altered expressions and because of their post transcriptionally regulatory role could provide favorable diagnostic, therapeutic, or prognostic values in head and neck cancers. Methods In this review, we have demonstrated diagnostic, prognostic, and potential therapeutic roles of some miRNAs associated with oral premalignant and malignant lesions based on previous validate studies. Results It is previously documented that dysregulation of miRNAs contributes to cancer development and progression. MiRNAs could be tumor suppressors that normally suppress cell proliferation, differentiation, and apoptosis or play as oncogenes that improved tumorigenesis process. Altered expression of miRNAs has also been reported in premalignant oral epithelial lesions such as leukoplakia, oral submucous fibrosis, oral lichen planus and some malignant carcinoma like oral squamous cell, verrucous, spindle cell, Merkel cell carcinoma and basal cell. Conclusion Some of miRNAs could be new therapeutic candidates in miRNA‐based target gene therapy. Although more investigations are required to identify the most favorable miRNA candidate, altered expression of some miRNAs could be used as biomarkers in premalignant lesions and oral cancers with high sensitivity and specificity.

periodontal disease, tooth movement and eruption, dental pulp physiology and pathology, dental cell differentiation, enamel mineralization, and cancerous lesions. 5 Specific miRNA expression profiles have been reported to be predictive of certain clinical outcomes in the oral cavity and could be used as biomarkers for diagnostic and prognostic purposes. 5 Previous studies have highlighted the potential diagnostic role of miRNAs in the management of oral diseases and cancerous lesions. 3, [6][7][8][9][10][11] In this review, we have described some alternations in the expression profile of miRNAs that can apply as novel biomarkers in disease control and predicted survival in head and neck premalignant and malignant lesions. The aim of this study is a description of the remarkable role of some miRNAs as diagnostic, prognostic biomarkers, and a potential candidate in therapeutic approaches of different head and neck lesions. In this manner, the miRNA types and their target genes with function are mentioned to highlight their alternation involved in lesion pathogenesis.
2 | THE PREMALIGNANT ORAL EPITHELIAL LESIONS

| Leukoplakia (leukokeratosis, erythroleukoplakia, erythroplakia)
Leukoplakia is a precancerous lesion that has histopathologic features, including hyperkeratosis with or without acanthosis. Some leucoplakias show epithelial atrophy. Epithelial dysplasia or carcinoma is found in about 5%-25% of oral leukoplakia. Dysplastic changes begin in the basal and supra basal epithelium. They mostly F I G U R E 1 The process of miRNA synthesis in oral epithelial mucosal that some of them affect extracellular binding proteins. miRNAs, microRNAs. located in the oral cavity after the age of 40. It's clinical appearance varies from persistent white plaques, thin, smooth leukoplakia to advanced erythroplakia. 2,12 It is assumed that consumption of tobacco, alcohol, sanguinaria, exposure to ultraviolet radiation, certain infections, and trauma may predispose its formation.
Cytogenetic and molecular changes associated with leukoplakia include loss of heterozygosity (LOH), microsatellite instability, increased telomerase activity, and upregulation of p53, p16, EFGR, MMR, and VEGF. 13 Moreover, altered expressions of some miRNAs such as miR-450b-5p, miR-21, and miR-1 have also been reported in the pathogenesis of leukoplakia, and associated with other cancers (Table 1). All these findings may apply as diagnostic, prognostic, and future therapeutic markers. 18

| Oral submucous fibrosis
Oral submucous fibrosis (OSMF) is a precancerous lesion characterized by chronic and progressive scar formation in oral mucosa likely due to disrupted collagen metabolism and consumption of areca nut (betel quid), nutritional deficiency, or tobacco smoking. The disease symptoms include trismus, stomatitis, and intolerance of spicy foods.
Histopathologic features are juxta epithelial and submucosal deposition of densely collagenized, hypovascular connective tissue along with the accumulation of chronic inflammatory cells. Mild cases are treated with intralesional corticosteroids, whereas moderate to severe cases require surgical splitting or excision of fibrous bands. 19 It is shown that expression of some molecular biomarkers such as miR-2, miR-31, miR-203, and miR-1246 changes following the formation of OSMF, which could be of great significance in the management of this lesion (Table 2).

| Oral lichen planus (OLP)
Lichen planus is a chronic inflammatory disease that may affect skin, genitalia, nails, and oral mucosa. Erosive lichen planus (ELP) is a variant of LP with painful ulcerations that is formed by autoimmune damage of the basal cell layer. The most common lesions of LP are purple papules with irregular borders and a pattern of white lines known as Wickham striae on their surface. Lesions of ELP present as atrophic, erythematous with central ulceration. 2 Histopathologic features include a saw-toothed rete ridge, hydropic degeneration of basal cell layer, and keratinocyte degeneration known as colloid bodies. However, the immunopathology characteristics of LP are not specific. There is also a potential malignant transformation of ELP to squamous cell carcinoma (SCC). Some cases present dysplastic leukoplakia, which is a secondary lichenoid inflammatory infiltrate that resembles OLP. 24 There is an association between hepatitis C and OLP particularly in specific populations of the Mediterranean region that highlights genetic profile and geographical distribution of LP. 25 An overexpression profile in some miRNAs like miRNA-146a/ miRNA-155 and miR-150-5p/miR-222-3p stimulate Th1 response in OLP, improve autoimmune disease which supports the contributory T A B L E 1 Some studies related to alternation in miRNA expression for Leukoplakia  Table 4, the regulation of some biomarkers such as miRNA is significantly disrupted in OSCC. Also, the profile of gene expression changes during OSCC process. 42,43 In Table 4  Subtypes include nodulocystic, pigmented, keratotic, adenoid, superficial, infiltrative, morphea form, and micronodular. In Table 5, we have listed alternations in the expression of miRNAs found in BCC.

| Merkel cell carcinoma
Merkel cell carcinoma is a rare, rapidly progressive neuroendocrine tumor that typically manifests as a painless nodule on the head or neck. contributing to its poor prognosis. 54 The miRNA expression profile of this tumor is demonstrated in Table 7.

| Sinonasal undifferentiated carcinoma (SNUC)
Sinonasal undifferentiated carcinoma is a rare and profoundly aggressive tumor with rapid development and a tendency to metastasize to multiple organs. It sometimes presents following radiotherapy of nasopharyngeal carcinoma or retinoblastoma. Immunohistochemically staining for cytokeratin or epithelial membrane antigen (EMA) is usually positive. The role of miR-21 in tumorigenesis has been previously reported in lung, breast, stomach, prostate, colon, and pancreas cancers. An increased expression of miR-21 is also found in undifferentiated sinonasal carcinoma suggesting its prognostic value in all these malignancies. 10

| Nasopharyngeal carcinoma
The nasopharyngeal carcinoma arises from epithelium of nasopharynx. Tobacco smoking, salt fish consumption, EBV infection,    and TGF-β1-induced type I collagen expression. This mechanism provides fibrogenesis in the oral cavity and also impacts liver, breast, and colon cancer progression 20 (Table 2). It has been proposed that miR-1246 can be a candidate for therapeutic approaches of submucosa fibrosis. 20 Overexpression of miRNA-146a/miRNA-155 and miR-150-5p/miR-222-3pstimulate Th1 response in OLP in encounter to an unknown autoantigen and manifest the imbalance of Th1/Th2 cytokines like IFN-γ production and also associate with tumor progression and lymph node metastasis. This cascade improves disease progression such as autoimmune disease (e.g., rheumatoid arthritis) (Table 3). 17,27 The miR-146a overexpressed in oral cancer and enhance tumorigenesis and also it associate with downregulation of NUMB endocytic adapter protein (NUMB), the IL-1 receptor associated with kinase 1 (IRAK1), and TNF receptorassociated factor 6 (TRAF6) ( Table 4). 41 On the other hand, some miRNAs play a role as tumor suppressors.
For example, miR-203 downregulated N-cadherin, vimentin, cell proliferation, and also increased CK19 and E-cadherin proteins. The miR-203 overexpression impedes arecoline-induced epithelial-mesenchymal transition and repressed proliferation-related genes that reported in some cancers such as breast, pancreatic, ovarian, laryngeal, and hepatocellular cancers 21 (Table 2). Thus, miR-203 can prevents invasion and be a candidate for future therapeutic approaches, because influences cell cycle-related genes, proliferation, and inflammation cascade, and also applied as a prognostic biomarker that affects survival rate in patients.
One of the other miRs that are known as tumor suppressor factor are miR-122 that has a critical role in inhibiting the tumorigenesis and angiogenesis in OLP and let-7d that preventthe tumorigenesis process and downregulated in head and neck squamous cell carcinoma (HNSCC) (Tables 3,4). 35,39 Also miR-204 sole as tumor suppressor that involved in pathogenesis of relative common carcinoma of the maxillary sinus by targeting EphA7 gene. 55 The dual regulatory role of miRNAs generalizes to different tissues and provides complication in a selection of specific microRNA for therapeutic strategies. It seems induce the expression of miRNA with tumor suppressor function or decrease the expression of miRNA with an oncogenic role can help us to use them as valuable therapeutic biomarkers. In addition to therapeutic approaches, oral miRNAs expression profile could serve as prognostic biomarkers by extracting them from body fluids (e.g., saliva, plasma, and blood) following a disease process or a therapeutic intervention. 52,75 Prognostic evaluations help us develop effective drugs or detect drug resistance.

| CONCLUSION
The miRNAs are involved in a wide range of cancer pathogenesis and biogenesis and also can apply for early diagnosis and timely treatment that affect patient survival. The potential role of miRNAs as valuable biomarkers in diagnostic, prognostic, and potential therapeutic strategies in oral cancers can lead to appropriate early diagnosis of precancerous lesions, prevention of malignancy development, and improve disease prognosis. Although more investigations are needed to identify the beststandardized protocol for miRNA isolation, altered expression miRNAs could be used for mentioned strategies in head and neck cancers as biomarkers with high sensitivity and specificity. A comprehensive strategy can help us to discover miRNAs with sufficient specificity and sensitivity for therapeutic approaches.

ACKNOWLEDGMENT
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

CONFLICT OF INTEREST
The authors declare no conflict of interest. All authors have read and approved the final version of the manuscript, Dr. Nooshin Mohtasham as corresponding author had full access to all of the data in this study and takes complete responsibility for the integrity of the data and the accuracy of the data analysis.

DATA AVAILABILITY STATEMENT
Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

TRANSPARENCY STATEMENT
The lead author Nooshin Mohtasham affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.